The present invention relates to current switches, such as those utilized in phase-locked loops, and more particularly to a charge pump used with a current switch.
Current switches are utilized to supply a constant current to a load circuit, such as a phase-locked loop. The input voltage of a phase-locked loop""s voltage-controlled oscillator requires high precision, and when generating input voltage by charging or discharging capacitance proportional to phase difference, the current from a current source must be precisely supplied for charging/discharging purposes.
A need has developed for a charge pump for a current switch of a phase-lock loop circuit for accurately controlling the current sources In order to shorten the phase-locked loop loading, thereby substantially increasing the initial charging current and decreasing the charging current when the phase-locked loop controlling voltage reaches the loading (settled) range.
In accordance with the present invention, a charge pump for a current switch having at least one current source is provided. The charge pump includes a current summation circuit for generating an output to the current switch. A first current source supplies a first current to the summation circuit. A second current source selectively supplies a second current to the summation circuit. A switch connects the second current source to the summation circuit, such that the current source of the current switch is proportional to the output of the summation circuit.